The present invention relates generally to monitoring systems and, more particularly, to a circuit useful for measuring the ionic content of solutions.
The techniques for measuring the ionic content of water are properly divided according to the purity of the water; that is, whether the water is pure or impure. Each division has its own set of problems such that measurement techniques optimized for pure water monitoring are not suitable for impure water monitoring.
In the past two-element conductive probes have been used successfully in pure water situations because the inherent metal-to-water interface resistance is sufficiently masked by the high resistance found in pure water, so as to be negligible. However, as the water purity decreases, there comes a water purity level at which the interface resistance exceeds the allowable error, and other techniques must be utilized.
Prior art systems have attempted to solve the problem noted above by using magnetic and comparative measurement and four-terminal techniques. These solutions have been only partially successful because of limitations of error imposed by their character and/or the systems have been increasingly more complex so as to impose higher cost to achieve low measurement error. However, when the problem is viewed from the aspect of minimum cost versus accuracy, the double or four probe conductivity cell has the most promise.